f# - MailboxProcessor and exceptions

Question

I wonder, why MailboxProcessor's default strategy of handling exceptions is just silently ignore them. For example:

let counter =
    MailboxProcessor.Start(fun inbox ->
        let rec loop() =
            async { printfn "waiting for data..."
                    let! data = inbox.Receive()
                    failwith "fail" // simulate throwing of an exception
                    printfn "Got: %d" data
                    return! loop()
            }
        loop ())
()
counter.Post(42)
counter.Post(43)
counter.Post(44)
Async.Sleep 1000 |> Async.RunSynchronously

and nothing happens. There is no fatal stop of the program execution, or message box with "An unhandled exception" arises. Nothing.

This situation becomes worse if someone uses PostAndReply method: a guaranteed deadlock as the result.

Any reasons for such behavior?

Answer 1

There is an Error event on the MailboxProcessor.

http://msdn.microsoft.com/en-us/library/ee340481

counter.Error.Add(fun e -> printfn "%A" e)

Of course, you can do something like Tomas' solution if you want to exert fine control yourself.